Encapsulation Studies on closo -Dicarbadodecaborane Isomers in Neutral Tetrahedral Palladium(II) Cages.

The encapsulation of icosahedral closo -dicarbadodecaborane ( o -, m -, and p -carboranes, Cb ) as guest molecules at the intrinsic cavities of the three isostructural tetrahedral cages [{Pd 3 (N i Pr) 3 PO} 4 (Cl-AN) 6 ] ( 1 ), [{Pd 3 (N i Pr) 3 PO} 4 (Br-AN) 6 ] ( 2 ), and [{Pd 3 (N i Pr) 3 PO} 4 (H-AN) 6 ] ( 3 ) was studied. The formation of definite host-guest assemblies was probed with mass spectrometry, IR, and NMR spectral analysis. 2D DOSY 1 H NMR of the Cb ⊂Cage systems showed similar diffusion coefficient ( D ) values for the host and guest species, signifying the encapsulation of these guests inside the cage assemblies. The hydrodynamic radius ( R H ) derived from the D values of the host and guest species further confirmed the encapsulation of the Cb isomers at the cage pockets. The single-molecule energy optimization of the host-guest assemblies indicated the preferential binding of o - Cb as a guest inside the cages ( 1 - 3 ). The stabilization of these Cb guests inside these cages was further attributed to various possible nonclassical C-H···X-type interactions.